Because of the cost of new acid, and/or the cost of disposal of iron chloride liquor, the commercial use of hydrochloric acid as a leachant for ilmenite depends on the availability of a technically viable and cost-effective method of regenerating and recovering the hydrochloric acid.
Regeneration of hydrochloric acid is in common use in the steel industry world-wide. For example the acid is used for cleaning steel and wire before galvanising. This process is known as "pickling" and the resultant liquors, consisting largely of iron chlorides and some free acid, is known as "pickle liquor".
The regeneration technology uses either a spray roasting, (Ruthnet), process, or a fluidised bed, (Lurgi), process, both of which produce by-product iron. The reactions: EQU B(i) FeO+2HCl-&gt;FeCl.sub.2 +H.sub.2 O EQU B(i) 2FeCl.sub.2 +2H.sub.2 O+0.5O.sub.2 -&gt;Fe.sub.2 O.sub.3 +4HCl (gas)
are essentially similar to those involving ilmenite.
In both cases the acid can be regenerated by hydrolysis of the iron chlorides. Excess water is removed by heat, and the iron oxide as dust, or as a pellet by-product.
Although the hydrolysis reaction is exothermic (.DELTA.H800.degree. C.=-112.6kJ [-26.9kcal]) the quantity of water that has to be boiled off requires an external heat source.
The principal difference between regeneration of pickle liquor and ilmenite leach liquor is that a significantly greater volume of liquor has to be processed when ilmenite is leached in commercial quantities, than is commonly necessary in the steel industry.
Simplistically, this requires either a very much larger reactor or multiple reactors for an ilmenite leach operation, the size or number required depending on the volume constraints imposed by reactor design.
The volume of concentrated iron chloride liquor which can be injected into a Lurgi--type fluidised bed reactor is limited by the need to achieve uniform distribution of liquor over the whole fluid bed. A large increase in feed volume cannot be accommodated by simply increasing reactor size (diameter).
As an example, the leach liquor from a 50,000 tonnes per year synthetic rutile production facility is estimated at approximately 54 tonnes per hour. Using the Lurgi pickle liquor regeneration technology, 4 reactors would required. The system described herein would require only a single reactor.